Altec 1556a int schematic

Page 2

pan-Ma

I. "ON»OFF Switch
2. Talk Volume

3.

Listen Volume

4. Program - Listen ~ Toik Bar

6, Normal , Return Speech Bar
7. Phono - Aux. - Mtcro Switch

5. Intercom - Standby Switch

Note: When this control is used the switch on
13718 Call»in unit must be held in "call"
position.

PRIVACY CIRCUIT

One of the outstanding features of the Altec 1556A
ALTALK unit is the incorporation of a Privacy Cir-
cuit. The use of the Privacy Circuit assures privacy
(freedom from supervisory monitoring) in all remote
areas. A more detailed description of this feature
can be found on Instruction Sheet No. 13765, of
13718 Call-in Switch Plate Assembly.

ALL CALL

This facility is not furnished as part of the 1556A
or 1557A units, however the LC. - OFF - CHAN A
and CHAN B switch positions on the 1557A are
"bussed" and wired to the terminal panel for
connection of relay or manual switching facilities.

PROGRAM

Set Intercom-Standby switch control 5, to Standby
position; set Program-Listen-Talk bar, control 4 to
Program. Any radio program material (AUX) or
record player material (PHONO) will be heard thru
the Speaker-Microphone on the "Master". Establish
the sound level by adjusting Listen Volume, con-
trol 3.

Auxiliary and Phono input sources are connected to
pin jacks on the rear of the 1556A ALTALK unit,
and selection of desired input source is accom»
plished with Phono»Aux-Micro selector switch, con-
trol 7.

MICROPHONE

A high impedance microphone may be connected to
the phone jack at the rear of the 1556A "Master".
This microphone may be located remote from the
"Master for program pickup. When using micro-
phone in this manner control 7 must be in the
Micro position and the Program-Listen»Talk bar in
the Program position.

Note: When Phono-Aux»Micro inputs are in use
the "call-in feature is inoperative. After
use, return control 4 to Listen position
and control 5 to Standby position.

PAGE 2

Figure 1

SINGLE AND DUAL CHANNEL
PROGRAM DISTRIBUTION

Program material may be distributed simultaneously
with intercommunication facilities by adding sepa-
rate program amplifiers (Altec amplifiers such as
model 356A, 1568A, etc., are recommended). Block
diagrams. figures 2 and 3 show typical single and
dual channel systems.

In these systems program material is amplified
separately, permitting intercommunication service
thru the 1556A ALTALK to continue without pro-
gram interruption.

WIRING

Connect 2 conductor #22 AWG or larger twisted
pair between terminals 3 and 4 on 1556A terminal
strip to LC. terminals on 1557A Speaker Selector
Switch Panel.

Connect loudspeakers and 13718 Call-In Switch
Plate Assembly to 1557A Speaker Selector Switch
Panel using 2 conductor #22 AWG or larger
twisted pair to numbered terminals. (In many in-
stallations shielded pair cable may not be required
for this circuit.)

Call»in and Privacy circuit must be 2 conductor
shielded #22 AWG or larger twisted pair. Connect
conductors to terminals 1 and 2 and shield to
terminal 8 on 1556A terminal strip.

Note: Installation may be simplified by loop»
ing "cal|»in" circuit wiring from one
speaker location to another.

MAINTENANCE

Since the Altec 1556A ALTALK Amplifier utilizes
high quality parts, that operate within their speci»
fied ratings, the need for routine maintenance is
minimized.

In the event that the 1556A ALTALK fails to operate
properly, all external wiring should be checked
immediately, as loose wiring or inadequate con-
nections will result in noisy and intermittent opera-
tion. Be extremely careful that no exposed wires
come into contact with other wires, terminals, parts
of the chassis or any other metal surfaces.